taru-adjective, adverb taking the 'to' particle
roaring; booming; reverberating
Literary onomatopoeic word describing a deep, resonant, and continuous loud sound, such as thunder, cannon fire, or a large crowd. Often used in the form 殷々たる or 殷々と.
The thunder roared and echoed all around.
The booming sound of cannons filled the battlefield.
Variant without iteration mark; less common but valid.
The exact derivation is uncertain; the kanji 殷 is used for its meaning of 'rumbling' or 'booming', and the reduplication creates an onomatopoeic literary expression.